However, While 1...a5 2.Nb5 might put the Knight on an outpost, what else is it doing? You might have light pressure on d6, but first off, it's hard to add any more pressure on d6. Secondly, when you do take, if somehow you were able to win it, your d3 pawn becomes super weak, and you'll probably drop the pawn back to him eventually.

Also, you have to look at more than just the Knight, but also the residual effects. What happens if Black eventually trades Knights with you, whether it be via the blunt Na7 or something else? What if the Bishop trades itself on b5, so as not to allow Nb5xWherever, but instead, Whatever Takes Knight on b5. How would you capture back? Neither pawn capture is ideal.

However, if you go to d5, and Black ever trades on d5, White can recapture with the e-pawn, and White has the e4 square available as a launch pad for his pieces (such as the bad bishop on g2).

If Black doesn't trade on d5, the Knight controls more key squares around the King, like e7 and f6, instead of being out in la la land controlling a7.

Nb5 should not be a problem for Black. Just play normally, develop and prepare ... f5 and get either king side counterplay or play in the center. Adorjan - Arnason 1982 and Rytov - Balashov 1973 both ended as draws with this idea.

Against Nd5 I would play the short line above. Against Be3 f5 immediately, against Bd2 I would play Be6, Qd7 and against f4 I would do Bg4. Should be ok for black, after all it's a symmetrical position so not much is going on.